﻿<!DOCTYPE html>

<html lang="en" xmlns="http://www.w3.org/1999/xhtml">
<head>
    <meta charset="utf-8" />
    <title></title>
</head>
<body>
    <script>
        // includes()  返回数组中是否包含参数这个元素 
        var arr = ["a", "b", "c"];
        var n = arr.includes("a");
        console.log(n); // true/false
    </script>
</body>
</html>